The invention relates generally to telecommunications and more particularly to a system and method of sending Dual Tone Multiple Frequency (DTMF) tones through a Global System for Mobile Communications (GSM) network having an Internet Protocol (IP) based backbone transport network.
Dual Tone Multiple Frequency (DTMF) tones are used to allow a telephone network user to, for example, interact with voice mail systems, to perform electronic banking, or to direct the functioning of an Advanced Intelligence Network (AIN) service. Traditionally, in a Public Switched Telephone Network (PSTN), DTMF tones are generated by the terminal (hand set). However, in GSM, if DTMF tones were transmitted from a Mobile Station (MS) handset, the DTMF signals would be mutilated by the GSM voice transcoder, and could not pass recognizably through the network. Thus, for a MS in a GSM network to send DTMF tones, a tone generation request message (rather than the actual tone) is sent from the MS to a Mobile Switching Center (MSC). The tones are then typically generated by the MSC and sent to a destination device.
Networks utilizing Internet Protocols (IP) are readily available, offer defined system interface protocols, and have the ability to reliably transmit voice data. IP-based transport networks may also simultaneously support the transport of other data types, such as Internet traffic or voice over IP (VolP) traffic for wireline networks. IP transport networks typically have lower capital costs, lower recurring costs, and lower tariffs than traditional circuit-switched networks. Accordingly, IP networks may soon be used as a communications backbone suitable for providing a platform to carry GSM network traffic, thus providing the same functionality as a circuit-switched network at lower cost. The benefits provided by the IP network, however, comes at a cost.
Since the voice data is being carried through an IP network, the circuit-switched devices in the MSC are no longer operable. Therefore, the MSC cannot directly insert DTMF tones on request from the MS. Therefore, there does not exist a reliable system or method of transferring a DTMF tone through an IP based GSM network. Therefore, there exists the need for a system and method of sending DTMF tones reliably through a GSM based telecommunications network that uses an IP network as a backbone.
The present invention provides a system and method for reliably transferring DTMF tones through an IP based GSM network. In general, when a MS sends a DTMF request (typically a DTAP message called xe2x80x9cStart DTMFxe2x80x9d), it is processed in the IP network by an MSC. The MSC activates an internal software module and an appropriate gateway (for independent, remote, tone generation), and then a processor in the gateway directs the production of the DTMF signal towards the destination network or MS.
According to one aspect of the present invention, provided is a system for sending DTMF tones through an IP based GSM network. The system generally comprises a mobile switching center having a first logical application module which receives a Direct Transfer Application Part (DTAP) message and converts the DTAP message into a Device Control Message (DCM). The system also contains a gateway coupled to the mobile switching center and the IP transport network, and which has a second logical application module that directs the generation of the tone.
The system may provide the capacity for the first logical application module to process the DTAP message and send a corresponding device control message to the second logical application module. In addition, the second logical application module may send a failure message to the first logical application module when tone generation is not possible to attempt or the attempt fails (e.g. congestion in tone-generating equipment). The second logical application module may also select the tone generation method and direct the creation and routing of the tone to the interworking or destination communication system. The gateway of the system may be in communication with a PSTN, an IP network, or another MS.
The method of supporting DTMF tone sending in an IP based GSM network utilizes the steps of receiving a DTAP command from a GSM MS, converting the DTAP command at the MSC into a device control message to the gateway, instructing a tone generator to generate a tone, and sending the tone to the interworking communication system. The interworking communication system utilized in this method could be a PSTN or other circuit-switched network.
Likewise, another method of supporting DTMF tone sending in a IP based GSM network utilizes the steps of receiving a DTAP command from a GSM MS, converting the DTAP command at the MSC into a device control message to the gateway, and selecting a tone generator method compatible with the interworking IP network. The tone generator method could comprise the steps of ordering a tone generator to generate a tone delivered as voice payload to the interworking IP network. The voice payload may be in the form of UDP, RTP, or other standard IP-based payload format, in accordance with the voice payload format of the interworking IP network. Alternatively, the tone generator method could comprise the step of converting the device control message to an IP telephony control message that is routed to the interworking IP network""s control node (e.g. an H.323 Gatekeeper) for this call.
Alternatively, another method of supporting DTMF tone sending in an IP based GSM network could comprise the steps of receiving a DTAP command from a GSM MS, converting the DTAP command at the MSC into a device control message to the gateway, ordering a tone generator to generate a DTMF tone, and delivering the DTMF tone from the tone generator to a destination GSM MS.